Methods and arrangements for phase tracking in wireless networks

ABSTRACT

Logic may determine phase correction information from pilot tones. Logic may determine phase correction information from some of the pilot locations. Logic may process the shifting pilot tones for less than all of the pilot tones. Logic may process pilot tones at any location within orthogonal frequency division multiplexing (OFDM) packet. Logic may determine to process only pilot tones at the even or odd symbol indices or subcarriers. And logic may transmit a packet with a frame with a capabilities information field comprising an indication that a receiver may can process shifting pilot tones for phase tracking.

BACKGROUND

Embodiments are in the field of wireless communications. Moreparticularly, the present disclosure relates to phase tracking basedupon shifting pilot tones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an embodiment of a wireless network comprising aplurality of communications devices;

FIG. 1A depicts an embodiment of a table illustrating pilot tonelocations and processing pilot tones;

FIG. 1B depicts embodiments of orthogonal frequency divisionmultiplexing (OFDM) symbols in an OFDM packet transmission with shiftingpilot tones;

FIGS. 1C-D depicts embodiments of simulations comparing the processingof pilot tones for phase tracking only against phase tracking withchannel estimate updates;

FIG. 2 depicts an embodiment of an apparatus with pilot logic to processshifting pilot tones; and

FIGS. 3A-B depict embodiments of flowcharts to process pilot tones totrack the phase of the channel and to generate, transmit, receive,parse, and interpret communications.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of novel embodiments depicted inthe accompanying drawings. However, the amount of detail offered is notintended to limit anticipated variations of the described embodiments;on the contrary, the claims and detailed description are to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the present teachings as defined by the appended claims.The detailed descriptions below are designed to make such embodimentsunderstandable to a person having ordinary skill in the art.

Institute of Electrical and Electronic Engineers (IEEE) 802.11ah systemshave bandwidths currently defined are 1 MHz (MegaHertz) and a set ofdown-clocked IEEE 802.11ac rates, namely 2, 4, 8 and 16 MHz, where thedown clocking is 10×. The 1 MHz system may use a 32-point fast Fouriertransform (FFT). Of those 32 carriers, 24 will be used for data and 2for pilot. Additionally, a repetition mode is being included to extendrange.

One of the issues for IEEE 802.11ah wireless networks is that with thelower data rates of the IEEE 802.11ah system, and the added use case ofoutdoor sensor and offloading, the Channel Doppler effect becomessignificant for longer packets. For example, using the 1 MHz mode, apacket with moderate to large payload sizes can exceed tens ofmilliseconds. The packet times were much lower for the IEEE 802.11n/acsystem, which was largely designed for indoor use, and thus the channelwas assumed stationary over the entire packet. It has been shown thatfor modest Doppler, the IEEE 802.11ah system performance may be severelydegraded without additional training, or channel updates, during thetransmission of long packets.

Embodiments may use of known pilot symbol tones shifting across thebandwidth of the orthogonal frequency division multiplexing (OFDM)packet during transmission of the packet to allow receivers to track thephase correction information during the transmission of the packet.Thus, the phase correction information can be used to track channelphase with different tones.

IEEE 802.11ah devices may include, e.g., indoor and outdoor sensors andcellular offloading. Low cost devices are less likely to have stringentfiltering and advanced algorithm to compensate for channel interference.The presence of reflectors in the environment surrounding a transmitterand receiver may create multiple paths that a transmitted signal cantraverse. As a result, the receiver can receive a superposition ofmultiple copies of the transmitted signal, each traversing a differentpath. Each signal copy may experience differences in attenuation, delayand phase shift while travelling from the source to the receiver. Thiscan result in either constructive or destructive interference,amplifying or attenuating the signal power seen at the receiver. Theeffect of destructive interference is referred to as channel fading andthe fading can be detected by, e.g., variations in the signal-to-noiseratio (SNR). Strong destructive interference is frequently referred toas a deep fade and may result in temporary failure of communication dueto a severe drop in the channel SNR. The channel fading may alsosignificantly impair the ability to determine accurate phase rotationsby processing stationary pilot tones.

Embodiments implement pilot logic that determines phase correctioninformation from pilot tones. Some embodiments implement pilot logicthat determines phase correction information from some of the pilotlocations. In some embodiments, the pilot logic may process the shiftingpilot tones for less than all of the pilot tones. In severalembodiments, the logic may process pilot tones at any location withinorthogonal frequency division multiplexing (OFDM) packet. In furtherembodiments, the logic may determine to process only pilot tones at theeven or odd symbol indices or subcarriers. And, in several embodiments,the logic may transmit a packet with a frame with a capabilitiesinformation field comprising an indication that a receiver may onlyprocess shifting pilot tones for phase tracking and may not performchannel updates based upon channel state information determined byprocessing pilot tones.

In many embodiments, transmitters shift the location of the pilot tonesevery N symbols, where N may be a system parameter, setting, or a fixedvalue such as N=1 or N=2. Thus, the location of the pilot tones remainconstant for N symbols before shifting to the next location. In severalembodiments, a receiver may then use the N pilot symbols for phasetracking using an appropriate algorithm. Some embodiments describedherein may implement the pilot shifting with N fixed to a value of one,which it means the pilots would shift every symbol and theimplementation of a fixed value for N may also remove a need ofsignaling between transmitter and receiver to update the value of Nbecause the single value used at the transmitter may be predetermined.

Various embodiments may be designed to address different technicalproblems associated with phase tracking with shifting pilot tones. Forinstance, some embodiments may be designed to address one or moretechnical problems such as addressing impairments to stationary pilottones associated with channel fading for, e.g., low cost sensors thatmay be located indoors and have no appreciable impairment from a Dopplereffect.

Different technical problems such as those discussed above may beaddressed by one or more different embodiments. For instance, someembodiments that address impairments to stationary pilot tonesassociated with channel fading may do so by one or more differenttechnical means such as determining phase correction information basedupon shifting pilot tones, processing selected shifting pilot tones, andthe like.

Some embodiments implement Institute of Electrical and ElectronicEngineers (IEEE) 802.11 systems such as IEEE 802.11ah systems and othersystems that operate in accordance with standards such as the IEEE802.11-2012, IEEE Standard for Information technology—Telecommunicationsand information exchange between systems—Local and metropolitan areanetworks—Specific requirements—Part 11: Wireless LAN Medium AccessControl (MAC) and Physical Layer (PHY) Specifications(http://standards.ieee.org/getieee802/download/802.11-2012.pdf).

Many embodiments may be fixed, low cost sensors installed in a home orother fixed location that are not impacted by channel Doppler andoperating at 1 MHz. In fact, many embodiments facilitate low costthrough the improved performance, allowing some of the low costembodiments to implement low cost front-end receiver circuitry that doesnot perform continual channel estimates. However, embodiments are not solimited. Several may embodiments comprise access points (APs) for and/orclient devices of APs or stations (STAs) such as routers, switches,servers, workstations, netbooks, mobile devices (Laptop, Smart Phone,Tablet, and the like), as well as sensors, meters, controls,instruments, monitors, appliances, and the like. Some embodiments mayprovide, e.g., indoor and/or outdoor “smart” grid and sensor services.For example, some embodiments may provide a metering station to collectdata from sensors that meter the usage of electricity, water, gas,and/or other utilities for a home or homes within a particular area andwirelessly transmit the usage of these services to a meter substation.Further embodiments may collect data from sensors for home healthcare,clinics, or hospitals for monitoring healthcare related events and vitalsigns for patients such as fall detection, pill bottle monitoring,weight monitoring, sleep apnea, blood sugar levels, heart rhythms, andthe like. Embodiments designed for such services may generally requiremuch lower data rates and much lower (ultra low) power consumption thandevices provided in IEEE 802.11n/ac systems.

Logic, modules, devices, and interfaces herein described may performfunctions that may be implemented in hardware and/or code. Hardwareand/or code may comprise software, firmware, microcode, processors,state machines, chipsets, or combinations thereof designed to accomplishthe functionality.

Embodiments may facilitate wireless communications. Some embodiments maycomprise low power wireless communications like Bluetooth®, wirelesslocal area networks (WLANs), wireless metropolitan area networks(WMANs), wireless personal area networks (WPAN), cellular networks,communications in networks, messaging systems, and smart-devices tofacilitate interaction between such devices. Furthermore, some wirelessembodiments may incorporate a single antenna while other embodiments mayemploy multiple antennas. The one or more antennas may couple with aprocessor and a radio to transmit and/or receive radio waves. Forinstance, multiple-input and multiple-output (MIMO) is the use of radiochannels carrying signals via multiple antennas at both the transmitterand receiver to improve communication performance.

While some of the specific embodiments described below will referencethe embodiments with specific configurations, those of skill in the artwill realize that embodiments of the present disclosure mayadvantageously be implemented with other configurations with similarissues or problems.

Turning now to FIG. 1, there is shown an embodiment of a wirelesscommunication system 1000. The wireless communication system 1000comprises a communications device 1010 that may be wire line andwirelessly connected to a network 1005. The communications device 1010may communicate wirelessly with a plurality of communication devices1030, 1050, and 1055 via the network 1005. The communications device1010 may comprise an access point. The communications device 1030 maycomprise a low power communications device such as a sensor, a consumerelectronics device, a personal mobile device, or the like. Andcommunications devices 1050 and 1055 may comprise sensors, stations,access points, hubs, switches, routers, computers, laptops, netbooks,cellular phones, smart phones, PDAs (Personal Digital Assistants), orother wireless-capable devices. Thus, communications devices may bemobile or fixed. For example, the communications device 1010 maycomprise a metering substation for water consumption within aneighborhood of homes. Each of the homes within the neighborhood maycomprise a sensor such as the communications device 1030 and thecommunications device 1030 may be integrated with or coupled to a waterusage meter.

When the communications device 1010 transmits a packet to thecommunications device 1030 to notify the communications device 1030that, e.g., the communications device 1010 is buffering data for thecommunications device 1030, the communications device 1010 may transmitan orthogonal frequency division multiplexing (OFDM) packetencapsulating a frame 1014. The OFDM 1022 of the transceiver (RX/TX)1020 may generate the transmission with pilot tones shifting locationswithin the symbol indices of the transmission every N symbols. In someembodiments, the communications device 1010 may have previouslytransmitted an indication of the value of N to the communications device1030. In further embodiments, the value of N may be a fixed value. Insome embodiments, the value of N is fixed at a value of one.

In some of such embodiments, the communications device 1030 maycommunicate a capability such as a capability to process pilot tonesonly to track a phase of the channel by a bit in a capabilityinformation field to the communications device 1010. In severalembodiments, the capability bit may refer to a single bit or a bit thatis part of a pair of bits to indicate capabilities of the communicationsdevice. For instance, the pair of bits may indicate an: (a) ability toprocess shifted pilot tones (for channel estimate and/or phase rotationupdates), (b) ability to process shifted pilot tones only for phaserotation, (c) inability to process shifted pilot tones. In otherembodiments, one bit may indicate (a) ability to process shifted pilottones (for both channel estimate and/or phase rotation updates) or (b)inability to process shifted pilot tones where the bit, if set to 1, (a)is met, if set to 0, (b) is met, or vice versa.

The communications device 1010 may transmit the OFDM packet one symbolafter the other sequentially and every N symbols, the location of thepilot tones within the OFDM packet may change either sequentially orrandomly. In some embodiments, the location of the pilot tones may shiftby one symbol index, or, in other words, from one subcarrier to theadjacent subcarrier.

Pilot tone shifting is a process where the pilot tones are sequentiallyassigned to different subcarriers as a function of time. In manyembodiments, only a subset of subcarriers may be used for pilot tones ordata purposes (usable subcarriers). For example, the pilot tones may beused only on data subcarriers (e.g., sweep through with the pilot toneon a symbol by symbol basis), may avoid nulled subcarriers (e.g., DCsubcarriers and guard subcarriers), an, in some embodiments, may evenavoid data tones that are adjacent to guard or DC subcarriers, andfurther in some embodiments may avoid a subset of data tones, forexample all even numbered tones.

The pilot tones and their positioning can be based on channel conditionssuch as coding scheme, packet length, and the like. FIG. 1A depicts atable 1100 of pilot tone positions demarked by symbol numbers. Thefollowing discussion is for the 1 MHz systems and is an example. Thereare other allocations for the 2, 4, 8 and 16 MHz bandwidths.

The table 1100 shows a progression of symbols transmitted from thecommunications device 1010 to the communications device 1030 from 1 to13. The number of symbols is chosen in the present embodiment based uponthe number of data and pilot tones, or useable subcarriers, and thepattern of pilot locations in relation to the symbol indices repeatafter 13. In particular, the table 1100 illustrates two pilot tones foreach symbol number. One pilot tone travels between the −13 subcarrierindex and a −1 subcarrier index and the second pilot tone travelsbetween the 1 subcarrier index and the 13 subcarrier index. For example,the first symbol transmitted may be symbol 1, which has two pilot tones,one located at the subcarrier index −8 and one located at the subcarrierindex 6. The second symbol transmitted may then be symbol 2 with pilottones at the subcarrier indices −9 and 5. The third symbol transmittedmay then be symbol 3 with pilot tones at the subcarrier indices −10 and4 and these pilot tone shifts continue through symbol 13 at which thepilot tones are at the subcarrier indices −7 and 7.

As shown in the table 1100, the pilot tones are shifted or assigned todifferent subcarriers or frequency bins as a function of time, which isreferred to herein as the locations of the pilot tone. The time betweenshifts in the location of the pilot tones is N=1 in table 1100 so thepilot tones shift between locations between every symbol. The table 1100also illustrates the pilot tones changing by one symbol index at a timeand sequentially. However, not all embodiments may implement a locationfor pilot tones as a function of time that results in the pilot tonesshifting through subcarriers or frequencies sequentially. In otherwords, the location of the pilot tones may shift every N symbols {N=1,2, 3, 4 . . . , 8, . . . } but the shift in frequency/location may berandom within the subset of subcarriers rather than sequential. Theshifting of the pilot tones can also be based on the modulation andcoding scheme (MCS) used for transmission or on the packet length of thetransmission (i.e., channel conditions). Further, the amount of time theone or more pilot tones occupy a particular location could be based on amodulation and coding scheme (MCS) and the MCS may be selected based ona data rate and a level of robustness required by traffic type. After aset of pilot tones are assigned, the process illustrated by the table1100 is cyclic and may be repeated over any number of symbols greaterthan 13.

The communications device 1030 may receive the transmission from thecommunications device 1010 and may utilize phase correction informationdetermined by processing the pilot tones. In some embodiments, the pilotlogic 1043 of the communications device 1030 may comprise logic todetermine phase corrections to correct the residual phase error in thereceived OFDM symbols. In many embodiments, the pilot logic 1043 willcontinuously update the phase correction information with each symbolreceived.

In the present embodiment, the pilot logic 1043 may receive the OFDMpacket with pilot tones distributed across the bandwidth of the OFDMpacket in accordance with the table 1100. The table 1100 provides anexample of a pattern for 1 MHz system (32 tones FFT, 24 data and 2 pilottones in each symbol) based on which pilots travel one symbol to anothercovering the entire bandwidth after 13 symbols. The pattern repeatsperiodically to cover all symbols in a packet.

FIG. 1B illustrates an embodiment of the OFDM packet 1200 transmittedfrom the communications device 1010 to the communications device 1030.The OFDM module 1022 may generate different OFDM symbols for differentbandwidths such a 2 MHz, 4 MHz, 8 MHz, and 16 MHz and may generate theOFDM packet 1200 for a 1 MHz bandwidth channel, for transceivers such asthe transceivers of FIG. 1, corresponding to a 32-point, inverse Fouriertransform. The OFDM packet 1200 comprises 32 tones on 32 subcarriers,indexed from −16 to 15. The 32 tones, in this embodiment, include 24data tones, five guard tones, two pilot tones, and one direct current(DC) tone. The four lowest frequency tones are guard tones provided forfilter ramp up and filter ramp down. The index zero frequency tone isthe DC tone and is nulled, at least in part, to better enable thereceivers to employ direct-conversion receivers to reduce complexity. Asper a commonplace preferred practice, the DC is selected to be one ofthe two subcarriers closest to the middle of the frequency band. And thedata and pilot frequency tones are provided between indices −13 through−1 and indices 1 through 13.

The RF receiver comprises an OFDM module 1042, which receiveselectromagnetic energy at an RF frequency and extracts the digital datatherefrom. For 1 MHZ operation, OFDM 1042 may extract OFDM symbolscomprising 24 data tones, five guard tones, and one DC tone such as theOFDM symbol 1210 illustrated in FIG. 1B. In other embodiments, the OFDMsymbols may be encoded in other manners with different numbers of datatones, pilot tones, and guard tones.

Note that the OFDM packet 1200 comprises OFDM symbols 1210, 1220, 1230,through 1240 and the OFDM symbols correspond to the pilot tone patternillustrated in table 1100. In particular, the OFDM symbols 1210-1240illustrate a dot for each of the guard tones, which are also referred toas edge tones. There is one dot in the center of the symbols 1210-1240illustrating the position of the DC tone as subcarrier index 0, and theDATA/PILOT TONES are demarked with numbers that start at the subcarrierindex −13 on the left side through the −1 subcarrier index next to theDC tone at the 0 subcarrier index, and continue with subcarrier index 1adjacent to the DC index 0 through the subcarrier index 13 adjacent tothe guard tones on the right side.

The OFDM symbol 1220 illustrates the OFDM symbol index 6 in table 1100and the pilot tones are the emboldened arrows at subcarrier indices{−13, 1}. Note that the OFDM symbol 1210 has pilot tones at subcarrierindices {−1, 13} adjacent to the DC tone and the guard tones. The OFDMsymbol 1220 has pilot tones at subcarrier indices {−13, 1} adjacent tothe DC tone and the guard tones. The OFDM symbol 1230 has pilot tones atsubcarrier indices {−12, 2} adjacent to the location of the symbol indexthat is adjacent to the DC tone and the guard tones. And, the OFDMsymbol 1230 has pilot tones at subcarrier indices {−2, 12} adjacent tothe location of the subcarrier index that is adjacent to the DC tone andthe guard tones.

In further embodiments, the communications device 1010 may facilitatedata offloading. For example, communications devices that are low powersensors may include a data offloading scheme to, e.g., communicate viaWi-Fi, another communications device, a cellular network, or the likefor the purposes of reducing power consumption consumed in waiting foraccess to, e.g., a metering station and/or increasing availability ofbandwidth. Communications devices that receive data from sensors such asmetering stations may include a data offloading scheme to, e.g.,communicate via Wi-Fi, another communications device, a cellularnetwork, or the like for the purposes of reducing congestion of thenetwork 1005.

The network 1005 may represent an interconnection of a number ofnetworks. For instance, the network 1005 may couple with a wide areanetwork such as the Internet or an intranet and may interconnect localdevices wired or wirelessly interconnected via one or more hubs,routers, or switches. In the present embodiment, network 1005communicatively couples communications devices 1010, 1030, 1050, and1055.

The communication devices 1010 and 1030 comprise memory 1011 and 1031,medium access control (MAC) sublayer logic 1018 and 1038, and physicallayer (PHY) logic 1019 and 1039, respectively. The memory 1011 and 1031may comprise a storage medium such as dynamic random access memory(DRAM), read only memory (ROM), buffers, registers, cache, flash memory,hard disk drives, solid-state drives, or the like. The memory 1011 and1031 may store frames and/or frame structures, or portions thereof suchas structures for an association request frame, an association responseframe, a probe frame, and the like.

The MAC sublayer logic 1018, 1038 may comprise logic to implementfunctionality of the MAC sublayer of the data link layer of thecommunications device 1010, 1030. The MAC sublayer logic 1018, 1038 maygenerate the frames and the physical layer logic 1019, 1039 may generatephysical layer protocol data units (PPDUs) based upon the frames. Forexample, the frame builder may generate frames 1014, 1034. The physicallayer logic 1019, 1039 may encapsulate the frames with preambles togenerate PPDUs for transmission via a physical layer device such as thetransceivers represented by receive/transmit chains (RX/TX) 1020 and1040.

The communications devices 1010, 1030, 1050, and 1055 may each comprisea transceiver (RX/TX) such as transceivers (RX/TX) 1020 and 1040. Inmany embodiments, transceivers 1020 and 1040 implement orthogonalfrequency-division multiplexing (OFDM). OFDM is a method of encodingdigital data on multiple carrier frequencies. OFDM is afrequency-division multiplexing scheme used as a digital multi-carriermodulation method. A large number of closely spaced orthogonalsubcarrier signals are used to carry data as OFDM symbols. The OFDMsymbols are divided into several parallel data streams or channels, onefor each subcarrier and encoded with the subcarriers by which the OFDMsymbols will be transmitted to a receiving device such as twenty-fourdata subcarriers, five guard subcarriers, two pilot subcarriers, and oneDC subcarrier. Each subcarrier is modulated with a modulation scheme ata low symbol rate, maintaining total data rates similar to conventionalsingle-carrier modulation schemes in the same bandwidth.

An OFDM system uses several carriers, or “tones,” for functionsincluding data, pilot, guard, and nulling. Data tones are used totransfer information between the transmitter and receiver via one of thechannels. Pilot tones are used to maintain the channels, and may provideinformation about time/frequency and channel tracking. And guard tonesmay help the signal conform to a spectral mask. The nulling of thedirect component (DC) may be used to simplify direct conversion receiverdesigns. And guard intervals may be inserted between symbols such asbetween every OFDM symbol as well as between the short training field(STF) and long training field (LTF) symbols during transmission to avoidinter-symbol interference (ISI), which might result from multi-pathdistortion.

Each transceiver 1020, 1040 comprises an RF transmitter and an RFreceiver. The RF transmitter comprises an OFDM module 1022, whichimpresses digital data, OFDM symbols encoded with tones, onto RFfrequencies, also referred to as subcarriers, for transmission of thedata by electromagnetic radiation. In the present embodiment, the OFDMmodule 1022 may impress the digital data as OFDM symbols encoded withtones onto the subcarriers to for transmission.

FIG. 1 may depict a number of different embodiments including aMultiple-Input, Multiple-Output (MIMO) system with, e.g., four spatialstreams, and may depict degenerate systems in which one or more of thecommunications devices 1010, 1030, 1050, and 1055 comprise a receiverand/or a transmitter with a single antenna including a Single-Input,Single Output (SISO) system, a Single-Input, Multiple Output (SIMO)system, and a Multiple-Input,

Single Output (MISO) system. In the alternative, FIG. 1 may depicttransceivers that include multiple antennas and that may be capable ofmultiple-user MIMO (MU-MIMO) operation.

The antenna array 1024 is an array of individual, separately excitableantenna elements. The signals applied to the elements of the antennaarray 1024 cause the antenna array 1024 to radiate one to four spatialchannels. Each spatial channel so formed may carry information to one ormore of the communications devices 1030, 1050, and 1055. Similarly, thecommunications device 1030 comprises a transceiver 1040 to receive andtransmit signals from and to the communications device 1010. Thetransceiver 1040 may comprise an antenna array 1044.

FIGS. 1C-D depict embodiments of simulations 1300 and 1400 of theprocess implemented in the pilot logic 1043 to study the use oftraveling pilots in a scenario where Doppler is not present, and showthat use of shifting pilots for only phase tracking improves packeterror rate (PER) performance for the full scale of signal-to-noiseratios (SNRs). In FIG. 1C, the legend indicates graphs for (1) pilotsshift every 2 symbols which is N=2, (2) pilots shift every symbol whichis N=1, (3) no traveling (shifting) pilots and (4) pilots shift everysymbol which is N=1 and no channel estimation (meaning for phasetracking only). In FIG. 1D, the legend indicates graphs for (1) pilotsshift every symbol which is N=1, (2) pilots shift every other symbolwhich is N=2, (3) no traveling (shifting) pilots and no channelestimation in any of the graphs in FIG. 1D (meaning for phase trackingonly). These simulation cases were for modulation and coding scheme one(MCS1) (501 symbols, 1500-byte packet) in FIG. 1C and modulation andcoding scheme zero (MCS0) (173 symbols, 256-byte packet) In FIG. 1D at a1 MHz bandwidth using carrier offset of −13.675 parts per million (ppm)of an IEEE 802.11ah device. In FIG. 1C, the graph (3) curve, shows thatthe proposed method of using traveling pilots only for phase tracking(bypassing channel estimation) improves the performance of traditionalmethod of no traveling pilots (solid black curve) by almost 2 dB at the1% PER point.

It also shows that the performance of the proposed method is almost asgood as the cases where traveling pilots are also used to update channelestimation (note dashed and dotted black curves). FIG. 2 confirms theresults for the case of a shorter packet and MCSO.

FIG. 2 depicts an embodiment of an apparatus to generate, transmit,receive, and interpret or decode frames. The apparatus comprises atransceiver 200 coupled with Medium Access Control (MAC) sublayer logic201 and a physical layer (PHY) logic 250. The MAC sublayer logic 201 maydetermine a frame and the physical layer (PHY) logic 250 may determinethe PPDU by encapsulating the frame or multiple frames, MAC protocoldata units (MPDUs), with a preamble to transmit via transceiver 200. Forexample, a frame builder may generate a frame including a type fieldthat specifies whether the frame is a management, control or data frameand a subtype field to specify the function of the frame. A controlframe may include a Ready-To-Send or Clear-To-Send frame. A managementframe may comprise a Beacon, Probe Response, Association Response, andReassociation Response frame type. And the data type frame is designedto transmit data.

In many embodiments, the MAC sublayer logic 201 may comprise a framebuilder 202 to generate frames. The PHY logic 250 may comprise a dataunit builder 203. The data unit builder 203 may determine a preamble toencapsulate the MPDU or more than one MPDUs to generate a PPDU. In manyembodiments, the data unit builder 203 may create the preamble basedupon communications parameters chosen through interaction with adestination communications device.

The transceiver 200 comprises a receiver 204 and a transmitter 206. Thetransmitter 206 may comprise one or more of an encoder 208, a modulator210, an OFDM 212, and a DBF 214. The encoder 208 of transmitter 206receives and encodes data destined for transmission from the MACsublayer logic 202 with, e.g., a binary convolutional coding (BCC), alow density parity check coding (LDPC), and/or the like. The modulator210 may receive data from encoder 208 and may impress the received datablocks onto a sinusoid of a selected frequency via, e.g., mapping thedata blocks into a corresponding set of discrete amplitudes of thesinusoid, or a set of discrete phases of the sinusoid, or a set ofdiscrete frequency shifts relative to the frequency of the sinusoid.

The output of modulator 209 is fed to an orthogonal frequency divisionmultiplexing (OFDM) module 212. The OFDM module 212 may comprise aspace-time block coding (STBC) module 211, a digital beamforming (DBF)module 214, and an inverse, fast Fourier transform (IFFT) module 215.The STBC module 211 may receive constellation points from the modulator209 corresponding to one or more spatial streams and may spread thespatial streams to a greater number of space-time streams (alsogenerally referred to as data streams). In some embodiments, the STBC211 may be controlled to pass through the spatial streams for situationsin which, e.g., the number of spatial streams is the maximum number ofspace-time streams. Further embodiments may omit the STBC.

The OFDM module 212 impresses or maps the modulated data formed as OFDMsymbols onto a plurality of orthogonal subcarriers so the OFDM symbolsare encoded with the subcarriers. The OFDM module 212 may generatesymbols in which the pilot tones change location within the data/pilotsubcarriers every N symbols. In many embodiments, the OFDM module 212may generate symbols in which the pilot tones shift locations along thesubcarrier indices sequentially. In several embodiments, the pilot tonesmay shift locations every symbol. For instance, when the communicationsdevice 1030 in FIG. 1 responds to a transmission from the communicationsdevice 1010, the RX/TX 1040 may respond with OFDM packets in which thepilot tones shift every N symbols. In some embodiments, the value of Nmay match the value of N provided by the communications device 1010. Inother embodiments, the value of N may be a fixed value for thecommunications device 1030 and/or for the communications device 1010. Insome embodiments, the communications device 1010, which may be theaccess point, may use a value of N provided to the communications device1010 by the communications device 1030. And, in some embodiments, suchas during association between the communications device 1030 and thecommunications device 1010, the communications device 1030 may transmitan indication in a capability information field in a frame of a packetto inform the communications device 1010 that the communications device1030 only processes the shifting pilots for phase tracking and notchannel updates update the equalizer.

In some embodiments, the OFDM symbols are fed to the Digital BeamForming (DBF) module 214. Digital beam forming techniques may beemployed to increase the efficiency and capacity of a wireless system.Generally, digital beam forming uses digital signal processingalgorithms that operate on the signals received by, and transmittedfrom, an array of antenna elements. For example, a plurality of spatialchannels may be formed and each spatial channel may be steeredindependently to maximize the signal power transmitted to and receivedfrom each of a plurality of user terminals. Further, digital beamforming may be applied to minimize multi-path fading and to rejectco-channel interference.

The OFDM module 212 may also comprise an inverse Fourier transformmodule that performs an inverse discrete Fourier transform (IDFT) on theOFDM symbols. In the present embodiment, the IDFT may comprise the IFFTmodule 215, to perform an IFFT on the data. For 1 MHz bandwidthoperation, the IFFT module 215 performs a 32-point, inverse FFT on thedata streams.

The output of the OFDM module 212 may be up-converted to a highercarrying frequency or may be performed integrally with up-conversion.Shifting the signal to a much higher frequency before transmissionenables use of an antenna array of practical dimensions. That is, thehigher the transmission frequency, the smaller the antenna can be. Thus,an up-converter multiplies the modulated waveform by a sinusoid toobtain a signal with a carrier frequency that is the sum of the centralfrequency of the waveform and the frequency of the sinusoid.

The transceiver 200 may also comprise duplexers 216 connected to antennaarray 218. Thus, in this embodiment, a single antenna array is used forboth transmission and reception. When transmitting, the signal passesthrough duplexers 216 and drives the antenna with the up-convertedinformation-bearing signal. During transmission, the duplexers 216prevent the signals to be transmitted from entering receiver 204. Whenreceiving, information bearing signals received by the antenna arraypass through duplexers 216 to deliver the signal from the antenna arrayto receiver 204. The duplexers 216 then prevent the received signalsfrom entering transmitter 206. Thus, duplexers 216 operate as switchesto alternately connect the antenna array elements to the receiver 204and the transmitter 206.

The antenna array 218 radiates the information bearing signals into atime-varying, spatial distribution of electromagnetic energy that can bereceived by an antenna of a receiver. The receiver can then extract theinformation of the received signal.

The transceiver 200 may comprise a receiver 204 for receiving,demodulating, and decoding information bearing communication signals.The communication signals may comprise, e.g., 32 tones on a 1 MHzcarrier frequency with pilot tones that shift every N symbols. Forexample, a data collection station compliant with IEEE 802.11ah for afarm may periodically receive data from low power sensors that haveintegrated wireless communications devices compliant with IEEE 802.11ah.The sensors may enter a low power mode for a period of time, wake tocollect data periodically, and communicate with the data collectionstation periodically to transmit the data collected by the sensor. Insome embodiments, the sensor may proactively initiate communicationswith the data collection station, transmit data indicative of acommunications capability, and begin communicating the data to the datacollection station in response to a clear-to-send (CTS) or the like. Inother embodiments, the sensor may transmit data to the data collectionstation in response to initiation of communications by the datacollection station.

The receiver 204 may comprise a fast Fourier transform (FFT) module 219.The FFT module 219 may transform the communication signals from the timedomain to the frequency domain.

The receiver 204 may comprise a pilot logic 250 comprising a channelestimator 252, a phase tracker 254, and an equalizer 258. The pilotlogic 250 may be configured for processing shifting pilot tones as wellas data tones. The receiver 204 may comprise an equalizer 258 withhard-coded logic or running an equalizer application or instructions, achannel estimator 252, and a phase tracker 254.

The baseband representation of the received data signals may bedelivered to the input of the equalizer 258, which filters the signalsin a manner dictated by the weighting function in accordance with theinitial weight coefficients set the equalizer 258 based upon the longtraining sequence in the preamble of the OFDM transmission. Theequalizer 440 may include any type of equalizer structure (including,for example, a transversal filter, a maximum likelihood sequenceestimator (MLSE), and others). When properly configured, the equalizer258 may reduce or eliminate undesirable channel effects within thereceived signals (e.g., inter-symbol interference).

The received data signals with pilot tones 210 are also delivered to theinput of the phase tracker 254. The phase tracker 254 may implement ajoint estimation algorithm for estimation of the carrier frequencyoffset and the timing frequency offset such as a weighted least squares(WLS) algorithm to track changes in phase over time using the pilottones as the pilot tones are rotated through each of the OFDMsubcarriers over the OFDM packet through time. As noted above, the pilottones are separated by some number of data subcarriers so thatestimation of slope and intercept for subcarrier tracking could bemaintained.

The receiver 204 may also comprise an OFDM module 222, a demodulator224, a deinterleaver 225, and a decoder 226, and the equalizer 258 mayoutput the weighted data signals for the OFDM packet to the OFDM module222. The OFDM 222 extracts signal information as OFDM symbols from theplurality of subcarriers onto which information-bearing communicationsignals are modulated. For instance, the OFDM symbols may comprise dataassociated with 24 data subcarriers, two pilot subcarriers, five guardsubcarriers, and one DC subcarrier.

The OFDM module 222 may comprise a DBF module 220, and an STBC module221. The received signals are fed from the equalizer to the DBF module220 transforms N antenna signals into L information signals. And theSTBC module 221 may transform the data streams from the space-timestreams to spatial streams. In one embodiment, the demodulation isperformed in parallel on the output data of the FFT. In anotherembodiment, a separate demodulator 224 performs demodulation separately.

The demodulator 224 demodulates the spatial streams. Demodulation is theprocess of extracting data from the spatial streams to producedemodulated spatial streams. The method of demodulation depends on themethod by which the information is modulated onto the received carriersignal and such information is included in the transmission vector(TXVECTOR) included in the communication signal. Thus, for example, ifthe modulation is BPSK, demodulation involves phase detection to convertphase information to a binary sequence. Demodulation provides to thedeinterleaver 225 a sequence of bits of information.

The deinterleaver 225 may deinterleave the sequence of bits ofinformation. For instance, the deinterleaver 225 may store the sequenceof bits in columns in memory and remove or output the bits from thememory in rows to deinterleave the bits of information. The decoder 226decodes the deinterleaved data from the demodulator 224 and transmitsthe decoded information, the MPDU, to the MAC sublayer logic 202.

Persons of skill in the art will recognize that a transceiver maycomprise numerous additional functions not shown in FIG. 2 and that thereceiver 204 and transmitter 206 can be distinct devices rather thanbeing packaged as one transceiver. For instance, embodiments of atransceiver may comprise a Dynamic Random Access Memory (DRAM), areference oscillator, filtering circuitry, synchronization circuitry, aninterleaver and a deinterleaver, possibly multiple frequency conversionstages and multiple amplification stages, etc. Further, some of thefunctions shown in FIG. 2 may be integrated. For example, digital beamforming may be integrated with orthogonal frequency divisionmultiplexing.

The MAC sublayer logic 201 may decode or parse the MPDU or MPDUs todetermine the particular type of frame or frames included in theMPDU(s).

FIGS. 3A-B depict embodiments of flowcharts process pilot tones to trackthe phase of the channel and to generate, transmit, receive, parse, andinterpret communications. Referring to FIG. 3A, the flowchart 300 maybegin with receiving an OFDM packet with pilot tones that shiftlocations of across the bandwidth of the packet (element 302). In manyembodiments, the OFDM packet may be received one symbol at a time andthe pilot tones may shift to a new location every N symbols, where N maybe a settable, calculated or fixed value. Thus, the pilot tones'locations may remain constant for N symbols before shifting to the nextlocation. In some embodiments, the value of N may be fixed a 1 or 2 sothe locations of the pilots shift after every symbol or after everyother symbol in the transmission.

After the receiver begins to receive the OFDM packet, the receiver maybegin to process the preamble of the OFDM packet to set initial weightcoefficients for equalization based upon a long training sequence in thepreamble of the packet (element 305). And then the receiver may begin toprocess pilot tones to repeatedly determine phase correction informationbased on pilot tones at different locations (element 310). For instance,in some embodiments, when the value of N is one, the receiver mayprocess pilot tones with the receipt of every symbol to determine newphase correction information based upon the new location of the pilot ineach symbol so the phase of the received symbols may be tracked.

The receiver may continue processing the packet with equalization basedon the initial weight coefficients while continuously updating phasecorrection information by processing the pilot tones throughout thetransmission of the packet so that the phase is continually tracked(element 310). In other words, the receiver may determine the locationsthat the pilot tones will shift to prior to receiving the pilot tones sothe receiver may comprise logic to process those pilot tones as thepilot tones move through the various subcarriers of the OFDM packet.Updating the phase tracking based upon pilot tones in all or nearly allof the subcarriers in the OFDM transmission averages the phase variationacross the subcarriers so the receiver can compensate for, e.g., carrierfrequency offset, timing frequency offset, and other impairments of thedata signals in the transmission.

Referring to FIG. 3B, the flowchart 350 begins with a receiver of astation such as the receiver 204 in FIG. 2 receiving a communicationsignal via one or more antenna(s) such as an antenna element of antennaarray 218 (element 355). The communication signal may comprise the pilottones that shift to new locations every N symbols. Thus, the pilot tonelocation remains constant for N symbols, then shifts to the nextlocation. The receiver may then use the N pilot symbols for phasetracking using an appropriate algorithm.

The receiver may convert the communication signal into one or more MPDUsin accordance with the process described in the preamble (element 360).More specifically, the received signal may be fed from the one or moreantennas to a pilot logic such as pilot logic 250 for equalization andphase correction and then to a DBF such as the DBF 220. The DBFtransforms the signals into information signals. The output of the DBFis fed to OFDM such as the OFDM 222. The OFDM extracts signalinformation from the plurality of subcarriers onto whichinformation-bearing signals are modulated. Then, the demodulator such asthe demodulator 224 demodulates the signal information via, e.g., BPSK,16-QAM, 64-QAM, 256-QAM, QPSK, or SQPSK. And the decoder such as thedecoder 226 decodes the signal information from the demodulator via,e.g., BCC or LDPC, to extract the one or more MPDUs (element 360) andtransmits the one or more MPDUs to MAC sublayer logic such as MACsublayer logic 202 (element 365).

The MAC sublayer logic may parse and interpret the frame in each of theMPDUs. For instance, the MAC sublayer logic may parse and interpret theframe to determine the frame type and subtype.

The following examples pertain to further embodiments. One examplecomprises a method. The method may involve receiving an orthogonalfrequency division multiplexing (OFDM) transmission of a packet withpilot tones shifting locations between OFDM symbols; setting initialweight coefficients for equalization based upon a long training sequencein response to receiving a preamble of the packet; processing the pilottones during the OFDM transmission to determine phase correctioninformation based upon the pilot tones at different locations; andprocessing the packet with equalization based on the initial weightcoefficients, wherein processing the packet comprises repeatedlyupdating phase tracking in response to the incoming phase correctioninformation determined from the pilot tones.

In some embodiments, the method may further comprise transmitting aframe with a capability information field comprising an indication thatthe device updates phase tracking only with the pilot tones. In someembodiments, wherein receiving comprises receiving the OFDM transmissionwith pilot tones shifting every N OFDM symbols. In many embodiments,wherein receiving comprises receiving the OFDM transmission with pilottones shifting every OFDM symbol. In several embodiments, whereinreceiving comprises receiving the OFDM transmission via an antennaarray. In several embodiments, wherein processing the pilot tones todetermine phase correction information comprises determining phaserotations of the pilot tones. In several embodiments, wherein processingthe pilot tones during the OFDM transmission to determine phasecorrection information based upon the pilot tones at different locationscomprises determining the phase correction every N symbols, wherein thepilot tones shift to different locations every N symbols. And, in someembodiments, processing the pilot tones repeatedly during the OFDMtransmission to determine phase correction information based upon thepilot tones at different locations comprises determining the phasecorrection every other symbol.

Another example comprises an apparatus. The apparatus may comprise apilot logic to receive an orthogonal frequency division multiplexing(OFDM) transmission of a packet with pilot tones shifting locationsbetween OFDM symbols; set initial weight coefficients for equalizationbased upon a long training sequence in response to receiving a preambleof the packet; process the pilot tones during the OFDM transmission todetermine phase correction information based upon the pilot tones atdifferent locations; and process the packet with equalization based onthe initial weight coefficients, wherein processing the packet comprisesrepeatedly updating phase tracking in response to the phase correctioninformation determined from the pilot tones; and an OFDM module coupledwith the pilot logic.

In some embodiments, the apparatus may further comprise an antenna arraycoupled with the pilot logic to receive the orthogonal frequencydivision multiplexing transmission. In some embodiments, the apparatusmay further comprise logic to transmit a frame with a capabilityinformation field comprising an indication that the device updates phasetracking only with the pilot tones. In some embodiments, the pilot logiccomprises logic to receive the OFDM transmission with pilot tonesshifting every N OFDM symbols. In some embodiments, the pilot logiccomprises logic to receive the OFDM transmission with pilot tonesshifting every OFDM symbol. In some embodiments, the pilot logiccomprises logic to process the pilot tones, comprises logic to determinephase rotations of the pilot tones. In some embodiments, the pilot logiccomprises logic to process the pilot tones comprises logic to determinethe phase correction every N symbols, wherein the pilot tones shift todifferent locations every N symbols. And, in some embodiments, the pilotlogic comprises logic to process the pilot tones comprises logic todetermine the phase correction every other symbol.

Another example comprises a system. The system may comprise a receiverto receive an orthogonal frequency division multiplexing (OFDM)transmission of a packet with pilot tones shifting locations betweenOFDM symbols; set initial weight coefficients for equalization basedupon a long training sequence in response to receiving a preamble of thepacket; process the pilot tones during the OFDM transmission todetermine phase correction information based upon the pilot tones atdifferent locations; and process the packet with equalization based onthe initial weight coefficients, wherein processing the packet comprisesrepeatedly updating phase tracking in response to the phase correctioninformation determined from the pilot tones; and a transmitter totransmit a second OFDM transmission with pilot tones shifting locations.

In some embodiments, the system may further comprise an antenna arraycoupled with the receiver to receive the OFDM transmission and thetransmitter to transmit the second OFDM transmission. In someembodiments, logic to transmit a frame with a capability informationfield comprising an indication that the device updates phase trackingonly with the pilot tones. In some embodiments, the receiver compriseslogic to receive the OFDM transmission with pilot tones shifting every NOFDM symbols. In some embodiments, the receiver comprises logic toreceive the OFDM transmission with pilot tones shifting every OFDMsymbol. In some embodiments, the receiver comprises logic to process thepilot tones comprises logic to determine phase rotations of the pilottones. In some embodiments, the receiver comprises logic to process thepilot tones comprises logic to determine the phase correction every Nsymbols, wherein the pilot tones shift to different locations every Nsymbols. And, in some embodiments, the receiver comprises logic toprocess the pilot tones comprises logic to determine the phasecorrection every other symbol.

The following examples pertain to further embodiments. One examplecomprises a machine-accessible product. The machine-accessible productmay comprise a medium containing instructions for phase tracking withshifting pilot tones, wherein the instructions, when executed by theaccess point, causes the access point to perform operations, theoperations comprising: receiving an orthogonal frequency divisionmultiplexing (OFDM) transmission of a packet with pilot tones shiftinglocations between OFDM symbols; setting initial weight coefficients forequalization based upon a long training sequence in response toreceiving a preamble of the packet; processing the pilot tones duringthe OFDM transmission to determine phase correction information basedupon the pilot tones at different locations; and processing the packetwith equalization based on the initial weight coefficients, whereinprocessing the packet comprises repeatedly updating phase tracking inresponse to the phase correction information determined from the pilottones.

In some embodiments, the operations may further comprise transmitting aframe with a capability information field comprising an indication thatthe device updates phase tracking only with the pilot tones. In someembodiments, receiving comprises receiving the OFDM transmission withpilot tones shifting every OFDM symbol. In many embodiments, processingthe pilot tones to determine phase correction information comprisesdetermining phase rotations of the pilot tones. In several embodiments,processing the pilot tones repeatedly during the OFDM transmission todetermine phase correction information based upon the pilot tones atdifferent locations comprises determining the phase correction every Nsymbols, wherein the pilot tones shift to different locations every Nsymbols. And, in some embodiments, wherein processing the pilot tonesrepeatedly during the OFDM transmission to determine phase correctioninformation based upon the pilot tones at different locations comprisesdetermining the phase correction every other symbol.

In some embodiments, some or all of the features described above and inthe claims may be implemented in one embodiment. For instance,alternative features may be implemented as alternatives in an embodimentalong with logic or selectable preference to determine which alternativeto implement. Some embodiments with features that are not mutuallyexclusive may also include logic or a selectable preference to activateor deactivate one or more of the features. For instance, some featuresmay be selected at the time of manufacture by including or removing acircuit pathway or transistor. Further features may be selected at thetime of deployment or after deployment via logic or a selectablepreference such as a dipswitch or the like. A user after via aselectable preference such as a software preference, an e-fuse, or thelike may select still further features.

A number of embodiments may have one or more advantageous effects. Forinstance, some embodiments may offer reduced MAC header sizes withrespect to standard MAC header sizes. Further embodiments may includeone or more advantageous effects such as smaller packet sizes for moreefficient transmission, lower power consumption due to less data trafficon both the transmitter and receiver sides of communications, lesstraffic conflicts, less latency awaiting transmission or receipt ofpackets, and the like.

Another embodiment is implemented as a program product for implementingsystems, apparatuses, and methods described with reference to FIGS. 1-4.Embodiments can take the form of an entirely hardware embodiment, asoftware embodiment implemented via general purpose hardware such as oneor more processors and memory, or an embodiment containing bothspecific-purpose hardware and software elements. One embodiment isimplemented in software or code, which includes but is not limited tofirmware, resident software, microcode, or other types of executableinstructions.

Furthermore, embodiments can take the form of a computer program productaccessible from a machine-accessible, computer-usable, orcomputer-readable medium providing program code for use by or inconnection with a computer, mobile device, or any other instructionexecution system. For the purposes of this description, amachine-accessible, computer-usable, or computer-readable medium is anyapparatus or article of manufacture that can contain, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system or apparatus.

The medium may comprise an electronic, magnetic, optical,electromagnetic, or semiconductor system medium. Examples of amachine-accessible, computer-usable, or computer-readable medium includememory such as volatile memory and non-volatile memory. Memory maycomprise, e.g., a semiconductor or solid-state memory like flash memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk, and/or anoptical disk. Current examples of optical disks include compactdisk-read only memory (CD-ROM), compact disk-read/write memory (CD-R/W),digital video disk (DVD)-read only memory (DVD-ROM), DVD-random accessmemory (DVD-RAM), DVD-Recordable memory (DVD-R), and DVD-read/writememory (DVD-R/W).

An instruction execution system suitable for storing and/or executingprogram code may comprise at least one processor coupled directly orindirectly to memory through a system bus. The memory may comprise localmemory employed during actual execution of the code, bulk storage suchas dynamic random access memory (DRAM), and cache memories which providetemporary storage of at least some code in order to reduce the number oftimes code must be retrieved from bulk storage during execution.

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the instructionexecution system either directly or through intervening I/O controllers.Network adapters may also be coupled to the instruction execution systemto enable the instruction execution system to become coupled to otherinstruction execution systems or remote printers or storage devicesthrough intervening private or public networks. Modem, Bluetooth™,Ethernet, Wi-Fi, and WiDi adapter cards are just a few of the currentlyavailable types of network adapters.

What is claimed is:
 1. A method to phase track with shifting pilottones, the method comprising: receiving an orthogonal frequency divisionmultiplexing (OFDM) transmission of a packet with pilot tones shiftinglocations between OFDM symbols; setting initial weight coefficients forequalization based upon a long training sequence in response toreceiving a preamble of the packet; determining phase correctioninformation based upon the pilot tones during the OFDM transmission frommore than one of the OFDM symbols; and processing the packet withequalization based on the initial weight coefficients, whereinprocessing the packet comprises updating phase tracking in response tothe phase correction information determined from the pilot tones in themore than one OFDM symbols.
 2. The method of claim 1, further comprisingtransmitting a frame with a capability information field comprising anindication that a receiver updates phase tracking with the pilot tonesthat shift locations between OFDM symbols.
 3. The method of claim 1,wherein receiving comprises receiving the OFDM transmission with pilottones shifting every N OFDM symbols.
 4. The method of claim 1, whereinreceiving comprises receiving the OFDM transmission with pilot tonesshifting every OFDM symbol.
 5. The method of claim 1, wherein receivingcomprises receiving the OFDM transmission via an antenna array.
 6. Themethod of claim 1, wherein determining phase correction informationcomprises determining phase rotations of the pilot tones.
 7. The methodof claim 1, wherein processing the pilot tones during the OFDMtransmission to determine phase correction information based upon thepilot tones at different locations comprises determining the phasecorrection every N symbols, wherein the pilot tones shift to differentlocations every N symbols.
 8. The method of claim 1, wherein determiningphase correction information comprises determining the phase correctionevery other symbol.
 9. A device to phase track with shifting pilottones, the device comprising: logic to receive an orthogonal frequencydivision multiplexing (OFDM) transmission of a packet with pilot tonesshifting locations between OFDM symbols; set initial weight coefficientsfor equalization based upon a long training sequence in response toreceiving a preamble of the packet; determine phase correctioninformation based upon the pilot tones during the OFDM transmission frommore than one of the OFDM symbols; and process the packet withequalization based on the initial weight coefficients, whereinprocessing the packet comprises updating phase tracking in response tothe phase correction information determined from the pilot tones in themore than one OFDM symbols; and an OFDM module coupled with the logic.10. The device of claim 9, further comprising an antenna array coupledwith the logic to receive the orthogonal frequency division multiplexingtransmission.
 11. The device of claim 9, further comprising logic totransmit a frame with a capability information field comprising anindication that the device updates phase tracking with the pilot tonesthat shift locations between OFDM symbols.
 12. The device of claim 9,wherein the logic comprises logic to receive the OFDM transmission withpilot tones shifting every N OFDM symbols.
 13. The device of claim 9,wherein the logic comprises logic to receive the OFDM transmission withpilot tones shifting every OFDM symbol.
 14. The device of claim 9,wherein the logic comprises logic to process the pilot tones compriseslogic to determine phase rotations of the pilot tones.
 15. The device ofclaim 9, wherein the logic comprises logic to process the pilot tonescomprises logic to determine the phase correction every N symbols,wherein the pilot tones shift to different locations every N symbols.16. The device of claim 9, wherein the logic comprises logic to processthe pilot tones comprises logic to determine the phase correction everyother symbol.
 17. A system to phase track with shifting pilot tones, thesystem comprising: a processor, a radio, and one or more antennas; areceiver coupled with the radio to receive an orthogonal frequencydivision multiplexing (OFDM) transmission of a packet with pilot tonesshifting locations between OFDM symbols; set initial weight coefficientsfor equalization based upon a long training sequence in response toreceiving a preamble of the packet; process the pilot tones during theOFDM transmission from more than one of the OFDM symbols to determinephase correction information; and process the packet with equalizationbased on the initial weight coefficients, wherein processing the packetcomprises updating phase tracking in response to the phase correctioninformation determined from the pilot tones in the more than one OFDMsymbols; and a transmitter coupled with the radio to transmit a secondOFDM transmission with pilot tones shifting locations.
 18. The system ofclaim 17, further comprising logic to transmit a frame with a capabilityinformation field comprising an indication that the receiver updatesphase tracking with the pilot tones that shift locations between OFDMsymbols.
 19. The system of claim 17, wherein the one or more antennascomprise an antenna array coupled with the receiver to receive the OFDMtransmission and the transmitter to transmit the second OFDMtransmission.
 20. The system of claim 17, wherein the receiver compriseslogic to receive the OFDM transmission with pilot tones shifting every NOFDM symbols.
 21. The system of claim 17, wherein the receiver compriseslogic to receive the OFDM transmission with pilot tones shifting everyOFDM symbol.
 22. The system of claim 17, wherein the receiver compriseslogic to process the pilot tones comprises logic to determine phaserotations of the pilot tones.
 23. The system of claim 17, wherein thereceiver comprises logic to process the pilot tones comprises logic todetermine the phase correction every N symbols, wherein the pilot tonesshift to different locations every N symbols.
 24. The system of claim17, wherein the receiver comprises logic to process the pilot tonescomprises logic to determine the phase correction every other symbol.25. A machine-accessible product comprising: a medium containinginstructions to phase track with shifting pilot tones, wherein theinstructions, when executed by the access point, causes the access pointto perform operations, the operations comprising: receiving anorthogonal frequency division multiplexing (OFDM) transmission of apacket with pilot tones shifting locations between OFDM symbols; settinginitial weight coefficients for equalization based upon a long trainingsequence in response to receiving a preamble of the packet; processingthe pilot tones during the OFDM transmission from more than one of theOFDM symbols to determine phase correction information; and processingthe packet with equalization based on the initial weight coefficients,wherein processing the packet comprises updating phase tracking inresponse to the phase correction information determined from the pilottones in the more than one OFDM symbols.
 26. The machine accessibleproduct of claim 25, wherein the operations further comprisetransmitting a frame with a capability information field comprising anindication that a receiver updates phase tracking with the pilot tonesthat shift locations between OFDM symbols.
 27. The machine accessibleproduct of claim 25, wherein receiving comprises receiving the OFDMtransmission with pilot tones shifting every OFDM symbol.
 28. Themachine accessible product of claim 25, wherein processing the pilottones to determine phase correction information comprises determiningphase rotations of the pilot tones.
 29. The machine accessible productof claim 25, wherein processing the pilot tones during the OFDMtransmission comprises determining the phase correction every N symbols,wherein the pilot tones shift to different locations every N symbols.30. The machine accessible product of claim 25, wherein processing thepilot tones during the OFDM transmission comprises determining the phasecorrection every other symbol.